fotogelectronspectroscopie

Fotoelektronen spektroskopie, often abbreviated as PES, is a surface-sensitive technique used to study the electronic structure of materials. It works by measuring the kinetic energy of electrons emitted from a sample when it is irradiated with photons. The energy of the incident photons is known, and by measuring the kinetic energy of the emitted electrons, the binding energy of those electrons within the material can be determined. This binding energy is characteristic of the specific element and its chemical environment.

The fundamental principle behind PES is the photoelectric effect, described by Einstein's Nobel Prize-winning work. When a photon strikes a material, it can transfer its energy to an electron. If this energy is sufficient to overcome the binding energy of the electron to the atom or molecule, the electron will be ejected. The excess energy of the photon, after overcoming the binding energy, becomes the kinetic energy of the emitted photoelectron. The relationship is expressed by the equation: Photon Energy (hν) = Binding Energy (BE) + Kinetic Energy (KE) + Work Function (Φ). For many applications, the work function is considered or accounted for.

PES is a powerful tool for elemental and chemical state analysis of surfaces. It can identify the elements present in a sample and provide information about their oxidation states and bonding environments. This makes it invaluable in fields such as materials science, chemistry, physics, and geology for characterizing thin films, catalysts, semiconductors, and biological samples. Different types of PES exist, including X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS), differing mainly in the energy of the photons used, which dictates the depth of information probed and the types of electronic states that can be analyzed. XPS typically probes deeper into the material, providing elemental and chemical state information, while UPS is more sensitive to valence band electronic structure.